In apparatuses which are driven by a battery, there is an apparatus controlled by a system which operates by the same battery. The system controls the apparatus which is driven by the battery using a computer.
When a residual quantity of a battery decreases, a voltage of the battery decreases by the own internal voltage drop. In case that the voltage of the battery becomes not more than the operation guarantee voltage, the computer is automatically reset for shutdown and then restarted for power-on.
When the computer is restarted, the apparatus which is driven by the battery is initialized. Usually, when the system is reset, as the power consumption of the system is sufficiently small, the battery voltage is restored. But, each time the system and the apparatus which is driven by the battery are initialized, the power consumption gradually increases. In case that the power consumption of the apparatus which is driven by the battery is sufficiently larger than the power consumption of the system, much power is consumed for the initialization of the apparatus in this time, and thereby the battery voltage decreases.
As a result, there is a problem that the computer falls into a state of repeating the reset and restart, and thereby it becomes impossible to control the apparatus which is driven by the battery. In addition, a problem and so on might be generated that the operation of the apparatus which is driven by the battery is disturbed, and thereby the degradation of the battery is accelerated.
For the reason, in conventional systems, there is a system which is provided a monitor circuit of the battery voltage so as to set the apparatus which is driven by the battery to a safe operation, in case that the voltage of the battery decreases below a reference value.
In addition, there is a system which is provided with a backup battery so as to continue to control the apparatus which is driven by the battery by switching to the backup battery, in case that the voltage of the battery decreases below a reference value.
However, the increase in the size of the system and increase in the power consumption of the system are brought, so that there is a problem that it is difficult to apply these systems to an apparatus in which miniaturization and low power consumption are required, such as a mobile device.